what is the hole is the ozone layer?

hi im doing a school project in geography about the hole in the ozone layer. the only problem is i have no idea what it is and ive tried looking for information about it in search engines and typing in information about the hole in the ozone layer, but none of the sites i have been to actually explain what is it and what it does. i would really really appreciate it if you could email me back and explain what the hole in the ozone layer is and a little bit of information about it. thanks